This application claims the priority of Japanese Patent Application No. 11-103946, filed on Apr. 12, 1999, the entire contents of which is hereby incorporated herein by reference.
Not Applicable
Not Applicable
FIG. 17 is a front-surface sectional view of a conventional plasma processing apparatus possessing an inductively coupled plasma generation system. A vacuum chamber consists of a lower chamber 10 and an upper chamber 12, these two being in communication with one another. The lower chamber 10, which has a generally cylindrical shape, is made of metal. The upper chamber 12 constitutes a discharge chamber, and its sidewall includes a power lead-in window 14 which is made of a dielectric material. The power lead-in window 14 has the shape of a cylinder with, for example, an inner diameter of 362 mm and a height of 100 mm. Around the power lead-in window 14, a generally ring-shaped (loop-shaped) antenna 18 is disposed in a manner such that it surrounds this window 14. The top plate 16 of the upper chamber 12 is made of metal, and is grounded. The interior of the vacuum chamber can be pumped out via an exhaust port 20. Process gas is introduced from a gas delivery system 22 which is connected to the top plate 16. A substrate 26 which is to be processed is set on a substrate holder 24. When the substrate holder 24 is in position for plasma processing, its top surface (the surface on which the substrate 26 is set) is located near the lower end of the upper chamber 12 (the portion thereof which is in communication with the lower chamber 10).
The plasma processing apparatus of FIG. 17 is used in the following manner. Process gas is introduced into the vacuum chamber and maintained at a required discharge pressure of 100 Pa or less. In this state, high-frequency power with a frequency of 13.56 MHz is supplied to the antenna 18, and power is supplied into the upper chamber 12 through the power lead-in window 14. This results in the production of a plasma in the concentrations in the upper chamber 12. Active species in the plasma effect processing (e.g., etching or deposition of a film) of the substrate 26 which is carried by the substrate holder 24.
FIG. 19 is a perspective view of the antenna 18 which is used in the apparatus of FIG. 17. The antenna 18 is essentially ring-shaped and has, in a portion thereof, a cut-out constituting a power supply portion. The shape of the transverse section of the antenna 18 is that of a long, thin rectangle. In its transverse section, the dimension a in the vertical direction is 2 mm, and the dimension b in the horizontal direction is 15 mm. The dimension a in the vertical direction is the dimension measured parallel to the central axis of the cylindrical power lead-in window, and can be called the antenna width. The dimension b in the horizontal direction is the dimension measured normally to the central axis of the power lead-in window, and can be called the antenna thickness.
When high-frequency power with a frequency of 13.56 MHz is used when the antenna 18 is employed for the production of a plasma, a plasma can be produced by an almost perfect inductively coupled mode (see the disclosure of Japanese Laid-open Patent Application No. 8-203695). Since the area of the antenna 18 inner periphery portion which faces the plasma in the upper chamber 12 is small (i.e., since the antenna width a is small), it is possible to achieve plasma formation solely by a practically perfect inductively coupled mode, and so efficient plasma generation is possible.
FIG. 18 is a front sectional view which shows the state at the time of substrate change in the apparatus of FIG. 17. After the substrate holder 24 has been lowered, a gate valve 28 is opened to open a substrate transfer-in/out port 30, and replacement of the substrate 26 is effected using a suitable substrate transfer device (not shown). Since it is difficult to provide the substrate transfer-in/out port 30 in the power lead-in window 14 made of a dielectric, it is necessary to provide it in the lower chamber 10 and effect substrate 26 replacement after lowering the substrate holder 24 as described above.
The present invention relates to a plasma processing apparatus, and more particularly it relates to a plasma processing apparatus which has special features by which alternating-current power which produces a plasma is led into a vacuum chamber.
Generally, when plasma processing is effected in a vacuum chamber, a film is deposited on the inner wall surface of the vacuum chamber. For example, when an oxide film on a substrate is etched, a freon-based process gas is used, with the result that an organic film is deposited. Also, in a CVD process, a film is deposited on portions other than a substrate. A film which has been deposited on the inner wall surface of a vacuum chamber is liable to peel off if the temperature of this wall surface changes. This occurs because the coefficient of thermal expansion of the deposited film and the coefficient of thermal expansion of the inner wall surface of the vacuum chamber are different, and, consequently, stress is produced in the deposited film when the temperature of the vacuum chamber inner wall surface changes. The deposited film which has peeled off falls inside the vacuum chamber and becomes a source of dust particle contamination. In order to prevent peel-off of the deposited film due to stress, it is necessary to keep the vacuum chamber heated to a constant temperature.
In the plasma processing apparatus shown in FIG. 17, the power lead-in window 14 is used for leading in high-frequency power. However, since the power lead-in window 14 is made of a dielectric material, it is more difficult to heat it to a constant temperature than it is to thus heat the lower chamber 10 made of metal. Ways of heating the power lead-in window 14 include resistance heating, heating by light, and heating by a liquid medium, etc. However, the high-frequency electric field becomes strong in the vicinity of the power lead-in window 14, and this field becomes disordered by the electric circuit used in resistance heating or light heating using a lamp, in addition to which there is a risk of damage to the electric circuit used for heating, since high-frequency power is superimposed on it. Further, when ordinary quartz glass is used as a dielectric material, the heating efficiency is poor and it is difficult to effect uniform heating in a method of heating using light, since the quartz glass passes hardly any light of the infrared region. In heating using a liquid medium, the procedure is that the power lead-in window is made a double structure, and power lead-in window temperature control is effected by flowing a liquid medium in the space of this structure, but there is a risk of leakage of the liquid, and, in addition, the structure of the power lead-in window is complex. Thus, it is not easy to heat the power lead-in window uniformly. However, if the power lead-in window is not heated uniformly, the risk of a film which has been deposited on the inner wall surface of the power lead-in window peeling off because of stress increases.
Since, accompanying the increase of the area of substrates, there is a trend to increase the area of power lead-in windows, a temperature gradient is liable to be produced in a power lead-in window. This temperature gradient too is the cause of easy peel-off of a deposited film. Further, when a power lead-in window made of a dielectric material is made larger, there is an increased risk of breakage.
Thus, in a conventional plasma processing apparatus, when a film has been deposited on the inner wall surface of the power lead-in window made of a dielectric, it is difficult to prevent peel-off of the deposited film.
The present invention has been devised for the purpose of resolving the above problem, and one of its objects is to provide a plasma processing apparatus in which a film which has been deposited on a power lead-in window does not constitute dust particles affecting a substrate even if it peels off.
Another object of the invention is to provide a plasma processing apparatus in which there are few dust particles and which offers good economic efficiency.
A further object of the invention is to provide a plasma processing apparatus in which it is possible to effect substrate exchange at the location of a discharge chamber.
The plasma processing apparatus of the present invention possesses a special feature in a power lead-in section for leading into a vacuum chamber alternating-current power for the production of a plasma. This power lead-in section comprises a dielectric element, and at least a portion of the dielectric element is exposed in the internal space of the vacuum chamber. The exposed portion of the dielectric element is in a position which cannot be seen from the substrate-carrying surface of a substrate holder located in the position it is in at the time of plasma processing. It is located between the substrate-carrying surface of the substrate holder and an exhaust port of the vacuum chamber.
When the dielectric element portion of the power lead-in section is located in such a position, it is possible for the vacuum chamber portion which can be seen from the substrate to be made of metal material. It is easy to effect heating and maintain the vacuum chamber portion made of metal at a required temperature. Therefore, even if a film is deposited on this vacuum chamber portion, there is little or no production of film stress in the deposited film. Therefore, the deposited film is less likely to peel off from this vacuum chamber portion. A film which has been deposited on a dielectric element portion of the power lead-in section is more likely to peel off due to film stress caused by a temperature change than is a film on the above-noted vacuum chamber portion made of metal. However, since the power lead-in section is in a position which cannot be seen from the substrate and, further it is located downstream of the substrate, a deposited film on the power lead-in section will not fall onto the substrate, even if it becomes detached, and so it has no adverse effect as dust particles on the substrate.
Further, when the vacuum chamber portion which can be seen from the substrate is made of metal, it is easy to provide a substrate transfer-in/out port in this portion. The provision of a substrate transfer-in/out port in this location makes it possible to effect substrate exchange while leaving the substrate holder in the position it is in at the time of plasma processing. Therefore, there is no need for a substrate holder displacement mechanism, and the substrate holder can be simplified.
Further, if the dielectric element of the power lead-in section is used as a portion (a vacuum seal portion) of the vacuum chamber, the area of the dielectric element constituting a portion of the vacuum chamber can be made smaller than that in a conventional apparatus. Therefore, there is less risk of damage to the dielectric element, and safety is improved. Also, it is possible to effect the work of maintenance of the interior of the vacuum chamber simply by opening the vacuum chamber portion made of metal, without removing the power lead-in section. Maintenance work is therefore easy, since there is no need for power lead-in section fitting and detachment work in which care over handling is demanded.
A description of the invention in terms of the direction in which introduced gas flows is as follows. Making a definition of upstream and downstream in the line of flow when gas which has been introduced from a gas delivery system flows through the interior of the vacuum chamber, the substrate-carrying surface of the substrate holder is located upstream of the portion of the dielectric element of the power lead-in section which is exposed in the internal space of the vacuum chamber, and an exhaust port leading to a vacuum pump system is located downstream of this exposed portion.
A typical power lead-in section comprises an essentially ring-shaped antenna, and a dielectric element is present between this antenna and the internal space of the vacuum chamber. High-frequency power is supplied to this antenna. The antenna may be embedded inside the dielectric element or it may be located on the external atmosphere side of a window made of a dielectric. By way of another structure, the power lead-in section may be a rectangular waveguide which is essentially ring-shaped. In this rectangular waveguide, a window made of a dielectric is formed at a surface which is exposed to the internal space of the vacuum chamber, and microwave power is supplied to the rectangular waveguide.